1. Field of the Invention
This invention relates to an electric circuit preferably used in an electronic appliance, which has a circuit which is always supplied with an electric power and always operates, and a circuit which contains a non-operating period, that is, a period not supplied with electric power. An ultimate purpose of the electric circuit is for saving power consumption.
2. Prior Art
Electronic pocket calculators and so-called electronic notebooks, that include a clock function contain a clock circuit that must be always operated, and a circuit having an non-operating period, such as a processing circuit or central processing unit for controlling such clock circuit.
FIG. 1 is a block diagram showing a basic structure of an electric circuit 1 of the prior art containing the above-mentioned circuits. The electric circuit 1 contains a processing circuit 2 for performing various processing functions, a clock circuit 3, and a power supply 4. When a positive supply voltage Vs&gt;0 is generated from the power supply 4 and each circuit in the electric circuit 1 is supplied with a positive voltage power, the operation is as follows.
The processing circuit 2 and clock circuit 3 are energized by the power supply 4. The time clocked by the clock circuit 3 is read out by the processing circuit 2 through line lc, and is displayed in a display unit (not shown) such as liquid crystal display device. The supply voltage Vs supplied from the power supply 4 through line la is selected at a voltage higher than the minimum operating voltage of the processing circuit 2. This supply voltage Vs is also supplied to the clock circuit 3 through line lb.
When the power is turned on, the peak value of the signal delivered to the processing circuit 2 through line lc from the clock circuit 3 is determined by the supply voltage Vs applied to the clock circuit 3, and therefore in order to transmit the signal securely to the processing circuit 2, the clock circuit 3 must be energized with a relatively high voltage approximately equal to the supply voltage Vs. Therefore, the clock circuit 3 which is usually at a relatively low operating voltage is also energized with the supply voltage Vs.
In such electric circuit 1, when the power is cut off, for example, the line la is cut off for supplying electric power to the processing circuit 2 from the power supply 4. At this time, since the clock circuit 3 must always clock the time, the supply voltage Vs is applied to the clock circuit 3 from the power supply 4 through line lb even while the power to the processing circuit 2 is cut off.
Therefore, the clock circuit 3 is energized with a relatively high voltage of the supply voltage Vs although its operating voltage is relatively low, and the power consumption is increased.
In such electric circuit 1, therefore, the power consumption increases, and when used, for example, in a portable electronic device, the power consumption of the battery used as the power supply 4 increases and the battery must be replaced very often. In addition, when a supply voltage of negative voltage is generated from the power supply 4, and each circuit in the electric circuit 1 is energized with a negative voltage, the same problem occurs.